1. Field
One embodiment of the present invention relates to a magnetic recording medium and a method of fabricating the magnetic recording medium, and a magnetic recording apparatus in which the magnetic recording medium is installed.
2. Description of the Related Art
In the modern information-oriented society, the amount of information has been increasing more and more. To keep up with this information-oriented society, there has been a demand for a recording/reproduction method with a dramatically increased recording density, and a recording/reproduction apparatus and a recording medium based on such a recording/reproduction method. To meet the demand, the recording medium is required to have smaller recording marks that are minimum units for writing information. At present, however, there is difficulty in reducing the size of each recording mark in the recording medium.
For example, in the case of a magnetic recording medium such as a hard disk drive, a recording layer includes a great number of magnetic crystal grains with a wide grain size distribution. However, owing to thermal fluctuation, recording with minute magnetic crystal grains becomes unstable. No problem will arise if the recording mark is large. However, if the recording mark is small, this leads to instability in recording or to an increase in noise. The reason for this is that if the recording mark is small, the number of magnetic crystal grains included in the recording mark decreases.
To avoid this problem, a magnetic recording medium called patterned medium is thought to be effective. In this magnetic recording medium, minute magnetic dots, which are composed of a recording material, are formed such that the minute magnetic dots are divided by non-recording regions. In the patterned medium, a single magnetic dot, which is divided by the non-recording region, becomes a single recording mark. Thus, interference between neighboring recording marks can be prevented.
There is an idea that a lithography technique is used in order to fabricate the patterned medium that includes divided magnetic dots, but there is a problem with this idea. Specifically, in the photolithography, a high throughput is obtained since batch-exposure is performed, but it is difficult to process sufficiently small recording cells. Besides, although micro-processing on the order of several-ten nm can be performed in electron-beam lithography or focused ion beam lithography, the throughput is poor in these techniques.
Under the circumstances, the following method has been studied as a method of fabricating the patterned medium at low cost. In this method, use is made of the phenomenon that a fine periodic structure is formed by the close packing of fine polymer particles or by the phase separation of a block copolymer. Using the fine periodic structure as a mask template, a magnetic film is processed, thereby forming an arrayed structure of divided magnetic dots.
In a method that self-assembling particles of the block copolymer are two-dimensionally disposed on the entire surface of a substrate, a structure that self-assembling particles are arrayed in a lattice fashion can be obtained. However, many defects and grain boundaries are present and lattices are randomly oriented. As a result, practical recording/reproduction cannot be realized.
In order to use patterns, which are obtained by the array of self-assembling particles, as magnetic dots of the patterned medium, there has been proposed a method in which concentric or spiral protrusions and recessed grooves, for instance, are provided on a disk substrate, and self-assembling particles are arrayed along the grooves (see Jpn. Pat. Appln. KOKAI Publication No. 2002-279616). The self-assembling particles are arrayed in the groove, with the crystal axis of the hexagonal lattice being aligned in the length direction of the groove. However, in this array process of self-assembling particles using the grooves, it is difficult to write servo patterns.
It is also possible to form servo patterns in advance as patterns of a magnetic material by some other lithography technique. In this method, however, the ratio of recesses to protrusions of the magnetic patterns differs between a data region which includes magnetic dots formed on the basis of self-assembling particles, and a servo region which includes a magnetic pattern formed by the other lithography technique. Consequently, there is a problem that vibration of the head occurs over the medium at the time of recording/reproduction, and the recording/reproduction becomes difficult.